As an automobile is being refueled with gasoline at a service station, each gallon of gasoline flowing into the fuel tank displaces approximately three hundred cubic inches of gasoline vapor which, unless collected, escapes into the atmosphere. Such vapors not only contribute to atmospheric pollution, but also are unpleasant to the person operating the nozzle, and may adversely affect the person's health over a longer term. As a result, some governmental authorities require that these vapors be collected. Various systems have been proposed and used for collecting and returning these vapors to a storage vessel, typically the underground storage tank from which the gasoline is being dispensed. The vapors thus stored are then collected for subsequent disposal by the over-the-road tanker when it delivers additional fuel to the storage tank.
In one such system, the dispensing pump nozzle is sealed to the filler pipe of the fuel tank so that the displaced vapor is directed by way of an annular conduit around the nozzle and coaxial dual conduit hose and appropriate plumbing to the underground storage tango. The design of the nozzle necessary to effect a seal has generally involved the addition of a bellows around the spout to seal the annular vapor passageway to the filler neck of the tank, as well as various other modifications which make the hand-held nozzle heavy and cumbersome, thereby causing the fueling process to be quite difficult and onerous, particularly for the self-serve motorist.
The problems relating to the design of the nozzle has been mitigated to a large extent by a system which utilizes a vacuum pump to assist the collection of vapor and transfer it to the storage tank. As a result of the use of the vacuum pump, it is unnecessary to seal the vapor line to the filler neck of the tank by the bellows, hence reducing the weight of the nozzle and simplifying the fueling process. In this type system, the vacuum inlet for the vapors need only be placed in close proximity to the filler neck of the tank. However, it is very important in this system that the rate of gaseous mixtures drawn in through the vacuum inlet closely approximate the volume of vapor being displaced by the gasoline flowing into the tank. If the volume of vapor being collected is less than that flowed from the tank, it will obviously result in some vapor escaping into the atmosphere. On the other hand, if a volume greater than the displaced vapors is collected, either air may be drawn in with the vapors, which can create a hazardous vapor/air mixture in the storage tank, or a portion of the gasoline dispensed into the tank will be vaporized to make up the difference between the volumetric displacement of the vacuum pump and the vapor displaced by the gasoline added to the fuel tank.
Several systems have been previously developed which utilized this system to achieve control of the appropriate ratio of vapor to liquid dispensed. In one such system, described generally in U.S. Pat. No. 4,202,385, a positive displacement vacuum pump is driven with a hydraulic motor, which in turn is driven by the flow of gasoline being dispensed to the tank. In another type system, a jet pump is driven by one of the submersible pumping units, for example, the regular grade, of the service station to generate a vacuum in a common vapor manifold.